Why built in microphone gets disabled with headphone ?

Hello Folks
I need your help
I used to have (HTC ONE S )and when i am in the car i connect my cellphone to AUX jack and i could hear incoming calls from car audio system, at the same time i was able to talk with phone's built in speaker which was pretty good.
I started using (Samsung Galaxy note 2) and i tried the same thing but unfortunately i hear the incoming voices from cars speakers but they cant hear me , it is like when i plug the 3.5 jack to car it disables built in microphone. i need to know if there is a option in setting or something that can help me with this issue .